The invention relates to systems and methods using solid state sensors for reading of optical codes such as UPC code.
Optical codes are patterns made up of image areas having different light reflective or light emissive properties, which are typically assembled in accordance with a priori rules. The term xe2x80x9cbar codexe2x80x9d is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Devices for identifying or extracting data from optical codes are sometimes referred to as xe2x80x9coptical code readersxe2x80x9d of which bar code scanners are one type. Optical code readers are used in both fixed or portable installations in many diverse environments such as in stores for check-out services, in manufacturing locations for work flow and inventory control and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by reading a target bar code from a printed listing of many bar codes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code reader includes a handheld sensor which is manually directed at a target code.
Most conventional optical scanning systems are designed to read one-dimensional bar code symbols. The bar code is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one dimensional bar code is the UPC/EAN code used to identify, for example, product inventory.
Bar codes can be read employing imaging devices. For example an image sensor may be employed which has a two dimensional array of cells or photo sensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor may be a two dimensional or area charge coupled device (CCD) and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view. A one-dimensional linear array of photodiodes is also known for use in detecting a bar code reflection image. See, e.g., U.S. Pat. No. 6,138,915 to Danielson et al.
It is known in the art to use a CCD photo detector and objective lens assembly in an optical code reader. In the past, such systems have employed complex objective lens assemblies originally designed for use in relatively expensive video imaging systems. Such systems may have a single sharp focus and a limited depth of field, which along with conventional aiming, illumination and signal processing and decoding algorithms, limits the versatility and working range of the system.
Other known imaging systems are designed primarily for reading optical codes. Such reading systems involve the assembly and alignment of several small parts. These parts may include a lens, an aperture and a 2D optical detector array such as a CCD chip. Such a structure is illustrated, for example, in U.S. patent application Ser. No. 09/096,578 for Imaging Engine and Method for Code Readers to Correa et al. filed Jun. 12, 1998 and assigned to Symbol Technologies, Inc. The Correa et al. application is hereby incorporated by reference herein.
It is an object of the present invention to further reduce the expense and difficulty associated with providing an optical code reading system.
It is known to provide illumination in optical code readers by employing illuminating devices to supplement ambient light. For example, U.S. Pat. No. 5,703,349 discloses an illumination module comprised of two lines of illuminating LEDs and lens cells. The above mentioned Correa et al. patent application also discloses an illumination system for a hand held optical code imager.
Existing one-dimensional imaging systems utilize off-the-shelf linear CCD detectors. A typical linear detector contains a few thousand pixels and has a total image length of about 28 mm. The focal length for a system using such a detector is approximately 38 mm assuming a field of view of 40 degrees. With a 0.4 mm wide by 6.2 mm high aperture the effective F-number (for light throughput) of the system is 21.4. Significant illumination is required for reasonable performance with such a system, and the device cannot be miniaturized.
It is a further object of the present invention to provide improved miniaturized code readers using one-dimensional solid state sensors.
Conventional code readers using one-dimensional sensor array require the code reader to be oriented so that the array is approximately parallel to the principle axis of the code being read. This may present problems during use in that the target object and/or the code reader may need to be realigned to produce a successful code reading.
It is a further object of the present invention to improve the ease with which a code reader which uses one-dimensional sensor technology can be aimed and aligned.
Conventional sensor array based code readers have employed a gun-shaped housing. However, such systems have required a relatively complex arrangement of circuit interconnections.
It is a further object of the present invention to interconnect and carry most or all of the circuit elements of a code reader on a single circuit board located in a gun-shaped housing.
These and other objects and features of the invention will be apparent from this written description and the drawings.
The present invention relates to apparatus useful in optical code readers.
One-dimensional solid state photo sensor arrays may be employed in these code readers. The terms xe2x80x9cone-dimensionalxe2x80x9d and xe2x80x9clinexe2x80x9d when used to describe arrays and sensors are intended to include linear arrangements of sensor cells including curved, segmented or straight lines of sensors cells. In preferred embodiments the arrays may contain relatively low numbers of cells for example about 1000 (e.g. a 1024 cell array) or about 500 (e.g. a 512 cell array), arranged in a straight line.
Systems of the present invention are particularly well adapted for reading a target one-dimensional optical code symbol whose principle axis has an arbitrary orientation in a plane generally parallel to an image plane of the sensor assembly. The system may include two or more photo sensor arrays each having cells arranged in a line, where the lines of the arrays are oriented at an angle to one another. This arrangement permits omni directional reading of one-dimensional optical code symbols. In order to read the code, the code reader is pointed at the code symbol so that the optical axis of the code reader is roughly perpendicular to a plane of the surface on which the symbol appears, but without regard to the orientation of the symbol in that plane.
A particularly preferred embodiment of the present invention employs three solid state photo sensor arrays each having cells arranged in a generally straight line are employed. The arrays produce electronic signals corresponding to at least a portion of the code symbol. The lines of the three arrays are oriented at an angle with respect to one another, preferably a 60xc2x0 angle.
A focusing system, such as a lens associated with each array, may be used to focus an image on each array. Where the focusing system includes three lenses, each one may have an optical axis which approximately intersects a mid point of the line of its respective photo sensor array.
The assembly may also include an electronic system for converting to digital form the electronic signals from the one of the sensor array whose line is most closely aligned with the principle axis of the target code symbol. Such an electronic system may include a sensor processor and software performing the function of a high blur digitizer. The selection of the data derived from the electronic signal from a particular one or ones of the sensors arrays may be made by attempting to digitize and decode electronic signals from each of the sensor arrays and using data from the first successful decode.
In one embodiment, each photo sensor array and processing circuitry is formed on a separately encapsulated semiconductor die. In another embodiment the plural photo sensor arrays are formed on the same die. The supporting circuitry for the photo sensor arrays may be located in the space on the die adjacent or between the arrays.
The assembly of preferred embodiments of the present invention may include solid state devices for producing an aiming beam for providing a reference spot on the target optical code symbol to be read. Advantageously, the aiming beam producing devices and the photo sensor arrays are carried on the same lead frame or circuit board. Advantageously, the aiming beam portion of the assembly comprises at least two LEDs and associated lenses for producing beams which converge to form a reference spot at a preferred focal distance for reading the target optical code symbol.
Systems of the present invention employ an optical assembly (typically an objective lens and aperture) for focusing light from a target optical code symbol on photo sensor arrays. Advantageously, the optical assembly has an F-number less than 8, preferably less than 5, more preferably less than about 3. An electronic digitizer may be implemented with a microprocessor and software for converting electrical signals to bit content for the target symbol. In preferred embodiments the digitizer is sufficiently powerful to extract bit content from a target symbol where the number of modules represented in the image focused on the photo sensor is less than or equal to the number of cells of the photo sensor. These systems may advantageously be incorporated in a miniature package having, for example, a focal length less than 5 mm and an overall volume of less than one cubic centimeter.
In a preferred embodiment of the present invention, the sensors and circuitry of the code reader are carried and interconnected by a single circuit board contained in a gun-shaped housing. The circuit board extends vertically through a head of the housing and through a backwardly and downwardly sloping handle portion of the housing. Advantageously, the circuit board carries one or more sensor arrays which define an optical axis of the sensor system. A principle plane of the circuit board is oriented substantially perpendicular to the optical axis and at an acute angle with respect to the backwardly and downwardly sloping handle portion of the housing. At least one interface connector for the code reader may be located at the lower end of the handle portion and circuit board.
The foregoing is intended as a convenient summary of the present disclosure. However, the aspects of the invention sought to be protected are set forth in the claims.